To establish a biological specimen bank within the ongoing Veterans Administration (V.A.) Cooperative Study #380, "Prospective Evaluation of Risk Factors for Large (greater than or equal to 1 cm) Colonic Adenomas." This bank will permit the examination of several nutritional and genetic hypotheses bearing on colorectal neoplasia. The V.A. Cooperative Study #380, "Prospective Evaluation of Risk Factors for Large (greater than or equal to 1 cm) Colonic Adenomas" is currently being conducted at 12 V.A. sites in the U.S. Phase I of the study examines characteristics of and risk factors for the presence of large and small polyps in 3,000 asymptomatic participants undergoing colonoscopy. Phase II involves an examination of factors associated with adenoma recurrence within a 5-year followup period among a subset of the original participants (all those with large and small polyps and a subset of polyp-free participants). The performance of complete colonoscopy on a large group of asymptomatic persons makes this study unique. In addition, the study is large enough to yield a substantial number of large adenomas. CPSB involvement has made possible the creation of a biologic specimen bank within this V.A. study that adds a valuable biochemical and molecular dimension to an important and unique study of large bowel neoplasia. Collaboration between CPSB and the V.A. involves the collection of blood and tissue specimens over the three-year study recruitment period. Specimens will be obtained from approximately 600 participants (an estimated 150 with large adenomas, 150 with small polyps, and 300 without polyps). White cells will be collected for future DNA analysis, and serum will be obtained for analysis of micronutrients or putative colorectal neoplasia markers. Two biopsies of normal-appearing tissue will be obtained from those participants with polyps. Approximately 3,000 participants have enrolled in the study. Over 10% of the participants have had large polyps (sample size calcultions were based on a 5% figure). CPSB investigators will lead or participate in cross-sectional analyses of serum micronutrients and molecular genetic markers in relation to presence or absence of large and small adenomas. Of particular interest is the potential interaction of dietary factors and genetic variants of metabolizing enzymes in the formation of colorectal neoplasms. These various biologic parameters will be examined later in relation to adenoma recurrence.